Jeff Riggenbach tells the story of how Nozick was won (at least temporarily) over to libertarianism:[1]

Ralph Raico, recalls first meeting or at least hearing about Robert Nozick in the very late 1950s or very early 1960s, through a mutual friend, who, like Nozick, was a graduate student of philosophy at Princeton. This mutual friend, Raico recalls, brought Nozick over to Rothbard's apartment one evening β "it must have been in the early 60s," he writes β for what turned out to be the first of many long nights of discussion and debate.

And those nights of discussion and debate were fruitful. β¦ This became evident in the fall of 1974 β¦ when a new book appeared on the scene amid considerable fanfare β a book called Anarchy, State & Utopia by Robert Nozick. In the opening pages, Nozick confessed to his readers that over the preceding several years he had "found myself becoming convinced of (as they are now often called) libertarian views" and that this process had been touched off by "a long conversation about six years ago with Murray Rothbard."

It is often contended that Robert Nozick 'lost' his libertarianism later on after the publication of Anarchy, State, And Utopia in his later work, The Examined Life, when he called the views espoused in his earlier work as "seriously inadequate." However, Robert Nozick argued against this assertion in a 2001 interview when he said, "What I was really saying in The Examined Life was that I was no longer as hardcore a libertarian as I had been before. But the rumors of my deviation (or apostasy!) from libertarianism were much exaggerated."